1. Field of the Invention
The invention relates to a heat conducting apparatus and a solder melting method, more particularly to a heat conducting apparatus for heating and melting solders between a soldered component and a circuit board through heat conduction or flow guiding, and a solder melting method for the apparatus.
2. Description of the Related Art
Referring to FIGS. 1 and 2, a circuit board 11 of a handheld electronic device (not shown), such as a mobile phone, a personal digital assistant, etc., generally has ball grid array (BGA) chips 12 soldered thereon. In order to conduct a rework operation on a chip 12′ to be repaired, a conventional rework machine (not shown) employs a hot air convection method to heat and melt solder balls 121 disposed between the chip 12′ and the circuit board 11, so that the chip 12′ can be removed for subsequent repair or replacement.
Since the circuit board 11 of the handheld electronic device has metal shells 13 soldered thereto to cover the chips 12, 12′ for shielding electromagnetic waves, the rework machine needs to melt solder pastes 131 disposed between the corresponding metal shell 13 and the circuit board 11 using the hot air convection method, so that the corresponding metal shell 13 can be removed to allow the subsequent rework operation on the chip 12′ to be repaired to proceed. However, during the process of causing hot air flowing out of an air outlet 141 of an air guide device 14 of the rework machine to heat the corresponding metal shell 13, the hot air may be blocked by the metal shell 13 or the circuit board 11 and change direction, so that electronic components 151 around the metal shell 13 and solder pastes 152 on the electronic components 151 may be heated by the hot air and become melted. Furthermore, some of the hot air may flow into the interior of the metal shell 13 via air vents 132 in a top end of the metal shell 13, which may lead to melting of the solder balls 121 of the chips 12, 12′ and the solder pastes 131 of the metal shell 13.
Referring to FIG. 3, in order that the convection range of the hot air from the rework machine can match the size of the chip 12′ to be repaired, a current approach is to design air guide devices having different sizes of air outlets for different sizes of chips, so that the air guide device can be replaced with one having a suitably sized air outlet to match the size of the chip 12′ to be repaired, thereby reducing the effect of the hot air on the other electronic components 151 or the good chips 12 during the rework process. However, this approach will increase the design and manufacturing costs of the air guide device considerably, which in turn will increase the cost of rework operations. Furthermore, since the hot air flowing out of the air outlet 141 (see FIG. 1) of the air guide device 14 is set to blow downwardly to the chip 12′, the blowing angle of the hot air is not adjustable. Therefore, the hot air will be blocked by the chip 12′ or the circuit board 11 and change direction, so that the electronic components 151 or the good chips 12 may be heated by the hot air, which may lead to melting of the electronic components 151 and the chips 12 or melting of the solder pastes 152 and the solder balls 121 of the chips 12, thereby resulting in loosening of the electronic components 151 and the chips 12. In more serious cases, the tiny electronic components 151 and the chips 12 may be blown away by the hot air and be lost, thereby lowering the rework quality.